1. Field of the Invention
The present invention relates to a gas laser oscillator in which laser gas is circulated in a laser tube, and from which a laser beam excited in a discharge area in the laser tube is output.
2. Description of the Related Art
In recent years, gas laser oscillators are widely used for drilling, cutting, welding or treating the surface of materials having a high hardness, and there is a great demand particularly in the area of factory automation.
One example of a conventional gas laser oscillator is shown in FIG. 11. The conventional gas laser oscillator of FIG. 11 is disclosed in the Gazette of the Japanese unexamined patent application No. Tokkai Hei 1-204486. FIG. 11 shows a schematic plan view of the conventional gas laser oscillator. The conventional gas laser oscillator comprises a laser tube 6 made of dielectric material such as glass, a total reflector 1 disposed at one end of the laser tube 6, return-beam reflectors 2, 3 for directing a laser beam 7 in the laser tube 6 and a partial reflector 4 disposed at the other end of the laser tube 6. As shown in FIG. 11, the laser beam 7 excited in the laser tube 6 is output through the partial reflector 4. The laser gas is led into the laser tube 6 from gas inlet ports 9, 11, 12 and 14, and exhausted from gas outlet ports 10 and 13. In FIG. 11, the directions of the gas-flow are indicated by short arrows. A pair of the laser tubes 6 are arranged in parallel, and connected in series so as to reflect laser beam 7 between the total reflector 1 and the partial reflector 4 via return-beam reflectors 2, 3.
As mentioned above, the conventional gas laser oscillator provides the gas inlet ports 9, 11, 12 and 14 adjacent to the total reflector 1, the return-beam reflectors 2, 3 and the partial reflector 4. The laser gas is supplied to the laser tube 6 via gas inlet ports 9, 11, 12 and 14 by a gas circulation apparatus thereby providing a high velocity gas-flow in the laser tube 6. That is, the total reflector 1, the return-beam reflectors 2, 3 and the partial reflector 4 are disposed in the gas flow. The laser gas includes floating powders, oil mists, dusts or the like brought from mechanical portions etc. of the gas laser oscillator. Such floating powders etc. are apt to stick to mirror portions of the total reflector 1, the return-beam reflector 2, 3 and the partial reflector 4. These mirror portions become more and more soiled with such powders etc. as time passes. As a result, the output of the conventional gas laser oscillator gradually decreases as time passes owing to the soiled mirrors.
Furthermore, because the total reflector 1, the return-beam reflectors 2, 3 and the partial reflector 4 are disposed near the discharge regions, which is formed between a respective pair of electrodes, these reflectors 1, 2, 3 and 4 are deteriorated by ultraviolet rays emitted from the discharge region, thereby decreasing the life time of the conventional gas laser oscillator.